In an ad hoc network, each entity or node of the network will communicate directly with its neighbors without passing through an infrastructure. If the destination is not in radio range of the source, the latter can pass its data through a string of other entities which will be responsible for forwarding them by virtue of a routing protocol embedded in each entity.
Networks comprising mobile entities communicating with fixed entities situated in the infrastructure are in general lower bitrate than ad hoc links but they benefit from a longer radio range. The capabilities for communication between the infrastructure and the mobile entities are very often critical and expensive resources (expensive for example as regards the quality of the global service which is manifested through a bandwidth requirement). When it is desired to transfer content to a large number of mobile entities, the network is then at risk of collapsing or the proposed service of becoming too expensive.
In the case of general-public telecommunications networks, the mobile entities, namely portable telephones, are endowed with connectivity to one or more networks of 3G (mobile telephone standard) and/or Wi-Fi infrastructure for example, and are also endowed with capabilities for ad hoc communication towards the other mobile entities (Bluetooth and/or Wi-Fi in ad hoc mode). The fixed entities, representing content providers for example, may be servers situated in the core of the Internet. In the terminology used in the present invention, the mobile entities are mobile users, while the content providers are both fixed users and pilots. The relay antennas and the routers of the operator network constitute the network scaffold.
In these hybrid networks, content can then be exchanged as is illustrated in FIG. 1a or in FIG. 1b from the pilot entities to the user entities or from the users to the pilot entities, see the arrows referenced F1 and F2, and between the user entities themselves, according to the arrow referenced F3. More precisely:
The arrow F1 corresponds to the dispatching of a content by a pilot entity 103k into the Internet, for example, to the user entities 101i. The transmission of the content that is to be distributed to a user who has subscribed to a service may be relayed from one user to another.
The arrow F2 corresponds to the dispatching of a mobile user entity 101i content to a pilot entity 103k. 
The arrow F3 is the exchange (the dispatching or the receipt of a content) between the mobile users 101i. 
Numerous communication paradigms or models may be put in place for these information exchanges, such as for example: the client-server model in which the fixed users host the content on servers to which the mobile users can connect so as to recover the content of interest to them. The mobile users search among the list of the contents available on the servers for those which interest them; the publication/subscription model known to the person skilled in the art consists of an asynchronous messaging where the senders (editors) of messages do not dispatch their messages to specific or subscriber receivers. Instead of this, the published messages are identified by classes. The subscribers express their interest in respect of the classes of messages that they wish to receive, without knowing, a priori, the published classes. This decoupling between the editors and the subscribers allows scaling and makes it possible to manage large dynamic swings in the network topology. The example chosen to illustrate the method according to the invention will be given within the framework of a publication/subscription model.
The users who have “subscribed” to a series of contents, or of information, in the manner of a subscription to an RSS stream (RSS designates a family of XML formats used for Web content syndication) may have reception timescale constraints. By way of example, people who have subscribed to the PDF (Portable Document Format) daily versions of a newspaper (for example, the New York Times) the information of which is relevant only on the day of publication, desire to receive the daily version before midday each day. These reception timescale constraints may be relaxed for other types of content, such as music titles (for example an MP3 file) of a given artist, or video documentaries (for example the history of France or other subjects).
The target services in respect of which the method and the system according to the invention may be applied are, for example, on-demand content services, by analogy with on-demand television (VoD, abbreviation of Video on Demand). These contents may be for example: software updates, videos (episodes of a TV series, documentaries), a newspaper in electronic version or publications of a blog.
In this context, the reduced number of communication channels between editors and subscribers prohibits the use of approaches such as multicast broadcasting (procedure for broadcasting information from a sender (single source) to a group (several supports/media). The massive distribution of one and the same content originating from a service provider/host and destined for mobile users is usually performed by broadcasting the content successively to each of the interested users. This poses problems of network scaffold loading, notably. The method of multicast type does not therefore allow massive distribution of content destined for mobile users while guaranteeing that the information content awaited by a user will arrive in a given timescale while minimizing the load on the network scaffold.
The publication/subscription model makes it possible to put data producers and consumers in touch, while minimizing exchanges through subscription and stream management mechanisms.
In most cases of use, the publication/subscription model is supported by message oriented middleware (MOM). The data distribution service for real-time systems (DDS) is, for example, a specification of a MOM operating on the publication/subscription model offering real-time guarantees on a local area network LAN. Such middleware provides a shared and omnipresent communication channel in modern information systems which allows numerous heterogeneous applications to integrate with one another and to exchange messages.
In the peer-to-peer (P2P) domain allowing several computers to communicate via a network and to share objects simply, numerous approaches have been proposed for distributing data while unburdening the content servers. An exemplary protocol known from the prior art allows an entity (called a seed) to share a content with a large number while reducing the impact in terms of bandwidth and processor use on itself. Users desiring to recover the content are called peers. Each peer, having recovered a part of the content, places it immediately at the disposal of the others.
In the type of network considered in this document, the topology changes regularly as dictated by the encounters between the mobile entities, and/or between the mobile entities and the scaffold of the network. The difficulty for the traditional implementations of the publication/subscription model is therefore to construct and to maintain the indices making it possible to put editors and subscribers in touch, and then to distribute the content from one point to another by passing the messages from one mobile entity to another as dictated by mobility.
For content routing in a network consisting solely of mobile entities, much work has been conducted in the field of networks tolerant to delays (DTN, Delay/Disruption Tolerant Networks). In DTNs, the nodes are mobile and encounter one another in an opportunistic or predictable manner. The number of neighbor nodes (with which a node is in contact) at each instant is fairly low and the connectivity graph is permanently partitioned. The probability of having an end-to-end path between a pair of nodes at a given instant is therefore very low (or indeed zero) when they are not in range of one another. It not being possible for the forwarding of the data packets to be done with the conventional IP routing mechanisms (e.g. Internet) in DTN networks, it may be based on the following principle: storage and transmission (known as “Store and Forward”). For example, the messages may be routed with an epidemic routing in which the messages propagate in an epidemic manner in the network. According to another type of routing of “Spray and Wait” type, the source node decides to transmit the message to N nodes that it encounters. Other known procedures of the prior art consider the historical log of the contacts which is used to determine whether or not it is opportune to retransmit a message.
It is also known to use a distributed algorithm making it possible to construct communities of users having similar mobility. The most central node of a community is elected broker so as to support disseminations of data of publication/subscription type within these communities.
In the publication by Stratis Ioannidis, Augustin Chaintreau and Laurent Massoulie, entitled “Optimal and Scalable Distribution of Content Updates over a Mobile Social Network”, Proc of INFOCOM 2009, Rio de Janeiro, Brazil, the authors study the dissemination of content flows (e.g., RSS streams) from a server in the infrastructure to mobile users in the hybrid networks supporting the epidemic dissemination of the content by using the ad hoc communication capabilities. The authors propose a procedure allowing the content provider to allocate mobile users a certain bandwidth on the infrastructure access network such that the global freshness of the content is a maximum, while being equitable in relation to the quantity of content received by the users. In this publication, the allocation of the resources on the infrastructure network is performed in a static and global manner by considering a unique source of contents. No control loop is used to reallocate the resources as a function of the actual performance observed.
Despite all the advantages that they exhibit, the known procedures of the prior art do not make it possible to tune the dissemination of the data over time as a function of the progress in this dissemination so as to comply with the required timescales, within which timescales the information must be delivered to a user.